Cyclotron target box cooler



y 5, 1955 c. DA.HUNT ET AL 2,712,223

CYCLOTRON TARGET BOX COOLER Filed March 31, 1952 2 Sheets-Sheet l FIG.

IN V EN TORS CHARLES D'A. HUNT HUBERTRYOCKEY ATTORNEY July 5, 1955 c. DA. HUNT ET AL 2,712,223

CYCLOTRON TARGET BOX COOLER Filed March 51, 1952 2 Sheets-Sheet 2 INVENTORS CHARLES D'A. HUNT BY HUBERT P. YOCKEY ATTORNEY United States Patent CYCLOTRON TARGET BOX COOLER Charles DA. Hunt, Orinda, and Hubert P. Yockey, Pasadena, Califi, assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application March 31, 1952, Serial No. 279,704

Claims. (Cl. 62-1) This invention pertains to cooling of a cyclotron target box, and particularly to a device for maintaining a target box at a temperature approximating the boiling point of liquid nitrogen.

The target of a cyclotron beam and the area immediately surrounding it experience a considerable rise in temperature which is disadvantageous for certain types of experimental work conducted with the cyclotron. In some experiments it is desirable to maintain the temperature of the target at a very low value, for example, at or below l50 degrees centigrade. This invention contemplates means for maintaining that temperature at a point approximating the boiling point of liquid nitrogen. At this temperature a cooling medium such as air would be undesirable because of its poor heat conductivity and the various gases present therein which might affect the results obtained from the experiment being conducted. Helium, which is an inert gas of relatively high heat transferring ability, is therefore used in this invention.

It is therefore an object of this invention to provide a cooling system for a cyclotron target box utilizing an inert gas as the cooling medium.

It is another object of this invention to provide means for cooling at target to a temperature of 150 C. While being irradiated by a cyclotron beam.

It is another object of this invention to provide cooling means adapted to maintain the temperature of the cooled region as near as possible to the temperature of the coolant.

It is another object of this invention to provide a cyclotron target box cooling system adapted to cool the target box to a temperature approximating that of boiling liquid nitrogen.

t is another object of this invention to provide a twostage cooling system having a maximum ratio of heat extracted to Weight of refrigerant evaporated.

It is another object of this invention to provide an improved heat exchanger for use in a two-stage cooling system for a cyclotron target box.

It is another object of this invention to provide a heat exchanger of minimum temperature differential between a relatively large flow of coolant and a small flow of fluid to be cooled.

Other objects of invention will become apparent from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a schematic diagram of the invention;

Fig. 2 is a sectional view of the heat exchanger of this invention;

And Fig. 3 is a sectional view of the device shown in Fig. 2 taken at 33 in Fig. 2.

Referring to the drawings, and in particular to Fig. 1, liquid nitrogen is periodically admitted through solenoid valves 1 and 2 by a device similar to that disclosed in patent application Serial No. 234,987, filed July 3, 1951, in the name of Robert E. Carter, for Electronic Liquid Level Controller, to an insulated nitrogen boiler 3 having an outer chamber 4 and an inner chamber 5 insulated from the outer chamber. Nitrogen boils in the outer chamber at atmospheric pressure, and at approximately ,4 atmospheric pressure in the inner chamber. The nitrogen vapor escapes from the outer chamber through conduit 6 connected to heat exchanger 7, and from the inner chamber through conduit 8 also connected to conduit 15 of heat exchanger 7. Conduit 15 contains a wire coil 16 provided for the purpose of causing turbulent flow therethrough, and therefore of increasing the heat transfer rate. It is to be noted that without coil 16, the Reynolds number of the gas is such that only laminar flow would exist. The vapor from the outer chamber escapes to the atmosphere through'conduit 9, and the vapor from the inner chamber is drawn off by vacuum pump through conduit 11. Target box 12 is cooled by helium carried to it by conduit 13. The helium which has been warmed slightly passes from target box 12 to conduit 14, thence to conduit 28 of heat exchanger 7 to compressor 18 which compresses the gas and expells it through conduit 19, which in turn is connected with an nular conduit 20 of heat exchanger 7 which contains conducting fins 21 extending radially between pipe 22 and pipe 23. Conduits 20 and 28 are provided with tubes 31 forced in between the heat exchanger fins so as to leave a very small space for gas flow through the conduits. These tubes are plugged at one end to prevent flow within the tubes. Upon reaching the right end of heat exchanger 7 the helium is within a few degrees of its boiling temperature at atmospheric pressure and is admitted to conduit 24 which conducts it to heat exchanger coil 25 in outer chamber 4 of the nitrogen boiler. In this chamber the helium is cooled to within one degree centigrade of the temperature of nitrogen boiling at atmospheric pressure, and is then admitted to coils 26 in inner chamber 5 where it is cooled to within .05 degree centigrade of the temperature of liquid nitrogen boiling at approximately atmospheric pressure. From this inner chamber the helium enters conduit 13 and thence to the target box to cool the target. Nitrogen vapor coming from the inner chamber of boiler 3 is conducted by conduit 15. Upon reaching the other end of the heat exchanger the nitrogen is exhausted to the atmosphere by vacuum pump 10. Nitrogen vapor from chamber 4 passes to the space between pipe 27 and pipe 29 of heat exchanger 7, and upon reaching the other end of the heat exchanger is exhausted to the atmosphere through conduit 9.

In operation, it can be seen by reference to Figs. 2 and 3 that the helium from the target box is carried by conduit of the heat exchanger, and in returning through spaces the entering helium is precooled by the action of the heat exchanger and is then admitted to the outer boiler where it reaches the temperature of liquid nitrogen boiling at atmospheric pressure. The helium is then further cooled by coils 26 within the inner chamber of the boiler to a temperature approximately equal to the temperature of liquid nitrogen boiling at approximately A atmospheric pressure. The helium then enters the target box'to cool the target. The nitrogen vapors from the outer chamber of the boiler flow through the outer jacket of the heat exchanger, thus preventing heat flow from the outside atmosphere into the cooler regions within the heat exchanger. Since the liquid nitrogen boiling in the inner chamber of the boiler is used only to cool the helium from the temperature of liquid nitrogen boiling at atmospheric pressure to the temperature of liquid nitrogen boiling at atmospheric pressure, it can be seen that this device offers a maximum of cooling per pound of liquid nitrogen utilized in the system. Turbulence within chamber 15 is attained by the use of wire coil 16, and within the space between pipes 27 and 29 by the use of coil 30. Cooling in conduits 20 and 28 is facilitated by the unusually large surface area provided by tubes 31 in conjunction with the fins. The heat exchanger is thus adapted to extract nearly all the heat from a small flow of helium, the heat being absorbed with very small temperature gradient by a larger flow of nitrogen. Thus, efiicient cooling by the heat exchanger is assured with a minimum size of heat exchanger. Since helium, an inert gas, is used as the cooling medium, no undesirable effects are experienced within the target box because of the presence of the cooling medium.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. Cyclotron target box cooling means comprising a nitrogen boiler having a liquid-tight outer chamber and a liquid-tight inner chamber enclosed by and insulated from said outer chamber, means for admitting liquid nitrogen periodically to said chambers, vacuum means for maintaining said inner chamber at reduced pressure,

means for venting said outer chamber to the atmosphere,

means for cooling a flow of helium by passing it through said outer chamber and then through said inner chamber without intermixture with the nitrogen therein, heat exchanger means for precooling said helium by means of efiiuent nitrogen gas from each of said chambers, and means for continuously circulating said cooled helium to said target box and back'through said heat exchanger to said boiler.

2. A device as recited in claim 1 in which said heat 'exchanger comprises four concentric cylinders in the inner and outer of which is placed a spiral wire for producing turbulence, the outer of which is connected to carry nitrogen vapor at atmospheric pressure, the second of which is connected to carry helium gas from said target box, the third of which is connected to carry helium from said circulating means to be introduced into said boiler, and the inner of which is connected to carry nitrogen vapor at reduced pressure whereby maximum cooling is achieved per pound of nitrogen evaporated.

3. A two-stage heat exchanger comprising a first conduit, a second conduit within said first conduit and spaced therefrom, a spiral wire in the space between said conduits, a third conduit spaced from and within said second conduit having a plurality of radial conducting fins thereon extending to contact with said second conduit,

a fourth conduit spaced from and within said third conduit and having a plurality of radial conducting fins thereon extending to contact with said third conduit, a pinrality of closed cylindrical tubes forced into the spaces between said fins, and a spirally Wound wire within said fourth conduit whereby if a first coolant gas is circulated through the space between said first and second conduits, if a second coolant gas at a lower temperature than said first coolant gas is circulated through said fourth conduit, and if a gas to be cooled is circulated first through the space between said second and third conduits and then through the space between said third and fourth conduits said gas to be cooled is cooled with a maximum of heat transfer to said cooling gases.

4. Cyclotron target box cooling means comprising a nitrogen boiler having a liquid-tight outer chamber and a liquid-tight inner chamber enclosed by and insulated from said outer chamber, means for admitting liquid nitrogen periodically to said chamber, vacuum means for maintaining said inner chamber at reduced pressure, means for venting said outer chamber to the atmosphere, conduit means passing through said two chambers in se- .ries for cooling helium gas first in said outer chamber and then in said inner chamber, a heat exchanger fabricated of concentric conduits having an outer conduit for carrying effiuent nitrogen gas from said outer chamber, an innermost conduit for carrying effiuent nitrogen gas from said inner chamber, and intermediate of large ratio of surface area to cross-sectional area conduits for carrying helium gas from said target box first adjacent said outer conduit and then adjacent said inner conduit, and means for circulating helium gas from said target box through said intermediate conduits, said outer chamber, said inner chamber, and said target box whereby a small flow of helium may be cooled to a minimum temperature by a larger flow of nitrogen gas in said heat exchanger and maximum cooling per weight of nitrogen evaporated is acheived.

5. In combination, a container to be cooled, a nitrogen boiler having a liquid-tight outer chamber and a liquid-tight inner chamber enclosed by and insulated from said outer chamber, means for admitting liquid nitrogen periodically to said chambers, vacuum means for maintaining said inner chamber at reduced pressure, means for venting said outer chamber to the atmosphere, means for cooling a flow of helium by passing it through said outer chamber and then through said inner chamber without intermixture with the nitrogen therein, heat exchanger means for precooling said helium by means of effluent nitrogen gas from each of said chambers, and means for continuously circulating said cooled helium to said container and back through said heat exchanger to said boiler.

References Cited inthe file of this patent UNITED STATES PATENTS 2,020,860 Touberg Nov. 12, 1935 2,361,075 Wiese Oct. 24, 1944 2,458,894 Collins Jan. 11, 1949 2,552,029 Bludeau May 8, 1951 2,553,142 McCreary May 15, 1951 

